The duplex mode of a Long Term Evolution (LTE) system mainly includes a Frequency Division Duplexing (FDD) mode and a Time Division Duplexing (TDD) mode.
In the TDD mode, the evolved NodeB (eNB) communicates with the User Equipment (UE) in the same frequency, wherein the uplink and downlink data transmissions are performed separately in time. Specifically, one wireless frame includes two half-frames each having five sub-frames. The TDD mode supports different uplink and downlink configurations, which can be adjusted semi-statically through the system messages according to the uplink and downlink average service requirement.
The LTE TDD system totally includes seven types of uplink and downlink configurations, as shown in Table 1, wherein “D” represents the downlink subframe, “U” represents the uplink subframe, and “S” represents the special subframe which is also used for the downlink data transmission.
TABLE 1Uplink anddownlinkSwitchingSubframe No.configurationcycle012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
Due to the characteristics of the wireless network, a data packet transmitted from the UE to the eNB may be lost or erroneous. When the eNB does not successfully receive the data packet from the UE, the eNB feeds back a NACK instruction to the UE, so as to instruct the UE to retransmit the data packet.
Currently, the data packet retransmission mechanism in the TDD mode is that when receiving the NACK instruction transmitted by the eNB, the UE retransmits the data packet to the eNB in an uplink subframe preconfigured in the standard and uniquely corresponding to the subframe where the data packet is initially transmitted. The retransmitted packet may be scheduled by an Uplink grant (UL_grant) transmitted by the eNB, or scheduled without the UL_grant.
In the LTE system, since the uplink and downlink configurations are semi-statically performed through the system messages according to the average service requirement, the uplink and downlink proportion of the configurations may be unmatched with the type of the instantaneous service, thus the resources cannot be utilized efficiently. For this reason, the subsequent release of the LTE system, such as Release-11 or 12, introduces the dynamic TDD subframe configuration, i.e., some subframes may be dynamically configured to be uplink or downlink, and these subframes are called as dynamical subframes or flexible subframes, and hereinafter are referred to as “dynamical subframes” for simplifying the descriptions.
Due to the introduction of the dynamical subframes, the data packet retransmission mechanism in the current TDD mode has the following problem.
When receiving the NACK instruction transmitted by the eNB, the UE retransmits the data packet to the eNB in corresponding uplink subframe. After introduction of the dynamical subframes, when the uplink subframe in which UE originally plans to retransmit the data packet to the eNB is a dynamical subframe, and the dynamical subframe has been adjusted as a downlink subframe by the eNB, a data transmission conflict will occur, and the UE cannot retransmit the data packet as originally planned, or the eNB cannot issue the data packet according to the original plan, thereby influencing data transmission performance and scheduling flexibility.